The present invention relates to a method of assembling an optical assembly having first and second longitudinal ends and comprising N coaxial shells forming individual mirrors, each of which extends between said first and second ends and presents a first diameter at said first end and a second diameter that is greater than the first at said opposite, second end, where the shells can be complete cylinders or cylindrical segments.
Such an optical assembly is known in particular as the WOLTER I type telescope mirror in which each individual mirror is a mirror for X-rays at grazing incidence, and is in the form of a surface of revolution having a region in the form of a parabola of revolution (adjacent to the larger-diameter second end) and a region in the form of a hyperbola of revolution (adjacent to the smaller-diameter first end).
Such an assembly and its method of integration is described in an article by D. de Chambure et al. entitled xe2x80x9cProducing the X-ray mirrors for ESA""s XMM spacecraftxe2x80x9d, published in ESA Bulletin No. 89 of February 1997, pages 68 to 79.
During integration, each shell, starting with the centermost shell, is measured and then positioned by its second end and fixed on a support, integration being performed from the center outwards.
The optical performance of each individual shell must be optimized prior to integration, which requires manufacture to very high standards of quality.
After integration, it is possible to monitor the optical performance of each shell forming the mirror, but it is not possible to make individual corrections to each shell. Unfortunately, the integration operation gives rise to deformation of the individual mirrors, if only because of gravity.
An object of the present invention is to provide a method of interaction which makes it possible to perform measurements and possibly to make corrections each time a new shell is integrated.
The invention thus provides a method of assembling an optical assembly having first and second longitudinal ends and comprising N coaxial shells forming individual mirrors, each of which extends between said first and second ends and presents a first diameter at said first end and a second diameter that is greater than the first at said opposite, second end, the method comprising:
1) putting the first end of the first shell situated outermost in the optical assembly into place on a support;
2) putting the first end of the second shell which is immediately adjacent thereto in the optical assembly into place on the support inside the first shell; . . . ; and
N) putting the first end of the Nth shell which is situated innermost in the optical assembly into place on the support.
Since the shells are integrated starting from the outermost shell and going inwards, with the shells being held on the support at least via their smaller-diameter ends, the inside surfaces of the shells, i.e. their active reflecting surfaces, remain accessible until the next shell is put into place, so it is thus possible to perform any corrective or additional operation that might be found suitable on each shell.
In particular, at least one of said installation operations comprises:
a) positioning one of said shells on the support;
b) measuring the topography of the inside surface of said shell as positioned on the support;
c) where appropriate, repositioning said shell on the support as a function of the result of said topography measurement; and
cxe2x80x2) fixing the position of said shell on the support.
In a preferred variant, at least one of said installation operations includes, after said fixing of its position on the support:
d) measuring the topography of the inside surface of said shell fixed on the support; and
e) where appropriate, ion machining the inside surface of said shell.
After e), it is particularly advantageous for the method to comprise:
f) applying a reflective coating on the inside face of said shell, and optionally, after f):
g) optically verifying said shell.
In said method, said topographical measurement is preferably implemented by differential measurement by scanning both, the inside surface of said shell and a reference cylinder placed on the support in a reference position, said differential measurement being performed without making contact by means of sensors which are carried by a measurement plate whose displacements are identified relative to said reference cylinder.
At least one shell can present at least one extension to at least one of its longitudinal ends.
In the method at least one shell can be constituted by a plurality of elements extending between the first and second ends, each element occupying a portion of the outline of said shell, and said elements can present at least one extension disposed at least one of the longitudinal ends thereof and at least one of the side edges thereof.
Such extensions constitute mechanical fixing elements. At least one of said extensions disposed at a longitudinal end can constitute a baffle for attenuating parasitic light.